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Three Transistor Voltage Detector…

Ahh yet another transistor project!! Well, this will be the last one for a while I promise.

This is an amplifier of sorts. In fact a viewer of the video posted below with the screen name MonkeyFCoconut summed it up very nicely with the following comment:“Pretty cool? man. I whipped up your circuit in LTSpiceIV and it seems to have a gain of 95 Million with still enough current to light the LED. This is basically a SUPER-Darlington Transistor The front end copper strip forms one side of a capacitor, and then when you bring it near a voltage potential a super tiny current flows between air dielectric of the “cap”. This is mega amplified with the high gain BC547′s and viola, the LED lights up. Might be able to detect pre-lightning strikes??”

This is a fun project to build and test out on different objects. It’s surprising what the thing will, “detect”

One thought on “Three Transistor Voltage Detector…”

You don’t specify the type of BC547 transistor you are using. There are three types, each with a different range of specified hFE. As per the Fairchild Semiconductor data-sheet the hFE ranges are: BC547A = 110 ~ 220, BC547B = 200 ~ 450, BC547C = 420 ~ 880. So if you use three BC547C’s instead of three BC547A’s your detector will be a lot more sensitive; it may even light the LED all the time just from the noise it picks up! You could get even higher gain by measuring the hFE of a bunch of BC547C’s and picking out the parts with the highest gain.